The cyclic hydroboration of dienes—a simple convenient route to heterocyclic organoboranes

Abstract

A systematic study of the cyclic hydroboration of a representative series of dienes with borane in tetrahydrofuran as well as with thexylborane is undertaken. The elucidation of the structures of the major products derived from 1.3-butadiene and borane and of the mechanistic paths leading to their formulation has been accomplished. Several new analytical techniques, such as gas-liquid partition chromatography examination of B-methoxyboracyclanes and the carbonylation-oxidation of organoboranes, are introduced. By employing these new techniques, the extent of cyclic hydroboration of a representative series of dienes with borane is determined. Based on the findings in this study, simple syntheses of representative bisboracyclanes. such as bisborinane and 9-borabicyclo [3.3.1] nonane, are accomplished. The hydroboration of olefins with these bisboracyclanes represents a convenient and general procedure for the preparation of the corresponding B-alkylboracyclanes. The cyclic hydroboration of dienes with thexylborane in many cases provides the corresponding B-thexylboracyclanes in high yields. Finally, the usefulness of B-alkylboracyclanes as valuable intermediates in the organic synthesis via hydroboration is briefly discussed. © 1972, Walter de Gruyter. All rights reserved.